Stay hydraulic. Most if not all all the 540 packages offered by builders use hydraulic. I realize you want to top the speed number the older mills put up before you dropped the serious coin on the current setup. At this point, I'd take whatever you get for a top end number in return for a trouble-free setup for years to come. As others have stated, now that you are aligned with a builder go with his recommendations based on your performance goals. No need to go wild on exotic parts for a mid 600 HP mill that can stay buttoned up for 300 hours.

Some of us want that every last bit. We want semi-radical lobes. So what do you do? Buy the best hydraulic lifter on the market? Well, the problem with that is availability. We ordered 3 sets of .904 hydraulics and 9 months later they were not yet available. Then you install them in a new motor spin the motor over 2 revolutions to adjust the valves. Prime it and start it up. Guess what... Not all the lifters pump up. Now what? Take two sets and make one? What about the other set you need for another motor? Now what? Wait another 9+ months to get another set. 2 years to build a motor? When the good ones work no doubt they work great. But do to the type of machining involved to make a performance oriented hydraulic sometimes you get a good set and sometimes you don't. The company that makes the good stuff has not increased there footprint in years but yet every year there sales go up and up. So what do you do? Again not all of us want stock warmed up motors. So you buy the best Solid lifter you can get your hands on use common sense when you set the valvetrain up and be responsible with maintenance of the valvetrain. Use parts that are easily accessible if a failure is getting ready to happen so you can have the parts the next day. A well setup solid lifter isn't any noisier than a hydraulic in a performance boat with dry exhaust that so loud you can here yourself think. That's my .02

All about preference in my opinion... But for all out top end power above 6k rpm, you can't beat a solid and that's proven. But for the every day guy/gal that I build engines for, the hydraulic in a lower rpm engine is best in my opinion.

For me, if I could have gotten to my center valve covers without it being a hassle (32 1/2" centers), I would have kept the solids. Over the years I've run solids in a few different engines I've built and for the most part was happy with the exception of one set (3) in a 42' Fountain back in the late 90's that had an aggresive Ultradyne solid in it that would beat the hell out of seats and lifters but made good power.

On the flip side, you guys should try adjusting your hydraulic lifters by bottoming them out and then backing off .020 which is determined by the pitch size of your studs. A lot of guys in the field have tested this method on spintrons including Kasse with excellent results over 7k rpm. Also, if you have a lifter not pump up or the plunger fail for some reason you only have .020 lash and it wont ruin the cam. Lastly, if you have one that wont pump up, remove the valve cover and adjust the rocker arm with the engine running. The lifter will pump right up a majority of the time. I ran into this a few years ago with a set of Johnson's. This process isn't in the service manual.

Panther, if you had say, a morel lifter, with .143 of plunger travel. Then adjust it down to .020 from bottoming out. If the lifter was to pump up, is there a risk of the valve and piston coming together?

Adjust the lash all the way down until the plunger bottoms out, then back off .020 based on your thread pitch. You're leaving .020 lash inside the plunger.

That's why you set your springs up close to coil bind...

(.143-0.20) x 1.7 = .2091

Yes, there would be that possibility if the valvetrain were to become unstable. As long as the valvetrain is well sorted out, I wouldn't see it happening as much say a manual trans street car and missing a shift. When that happens it goes over the RPM limit of the valvetrain, lofts/bounces and over pumps the lifter. Realistically if you wanted to run that little of travel, just buy a short travel. In essence it's achieving the same exact thing without the risk of PtV problems.

Usually when they don't pump-up it's because of a trapped air bubble. Running them deep sometimes works, or backing them off to almost 0 lash sometimes works. It happens more frequently with heavier oils...and usually all that's needed is oil temps getting up around 160-180.

That's basically what we do. The only problem with this is because the lifter must be honed to get the tolerances tight a lot of times there is taper. Once you run the cup down the taper in the lifter grabs the cup and your screwed the lifter will never come back up. Sometimes you can bang it on a block of wood and it will release but usually not. If the lifter had a hole all the way through the bottom the taper would be a problem cause you could run the hone all the way through but it's not so sometimes you get a good set sometimes you don't.

And thus the other issue with Hydraulics. Hot thin oil (less than 50wt) in a boat is a recipe for disaster.