I like the peterson single stage external pump for the wetsump deal... very nice pumps, and I use them on anything I build with wet sump, for a max effort deal.
As for hp limit? There is no hp, or rpm 'limit'.... you can make a wet sump work with high rpm just fine and in terms of 'hp'.... you can get real close to a dry sump but it's hard to beat the reliability, efficiency and resultant oil control of a dry sump. If I had the $$, and the room, I would do a dry sump.
Look at it this way.
Good wet Sump pump 600 bucks
GOOD Wet Sump pan 7-800 bucks
Vacuum Pump setup - 800 bucks all said and done the right way
Misc. lines and fittings another couple hundred bucks. You're looking at the potential of over 2 grand for a 'good' wet sump....
I assume you're talking something for Milan...