I shot a G34 in Production more than a few years ago! ... IMO, ya don't need to do anything with the trigger ... or sights ... or anything else!
That said, I also shot a G20 ... and while the slide certainly changed the feel, I preferred the shorter sight-radius ... and otherwise don't believe the extended cut-out G34/G35 slide offers significant benefit!
... if yer grip is that loose, a longer slide ain't the cure!
I'd definitely go with the gen 4 ... if ya end up shooting a lot, with other guns, ya may end up with a particularly high grip ... that's what the new gen 4 beavertails are for!
If ya go with a G17, then I'd definitely put a new connector in it!
CZ SP-01 is a good gun ... as is P226 ... and others ... what ya'll find is, the less ya spend, the more it costs to get a nice trigger in it! ... IMO, SRT P226 is GTG, outta the box!
Figure $100 - $150 more for a decent trigger in a M&P er XDM ... vs. a $30 connector for a Glock, I'd say that's a no-brainer!