how much gain for series 1 sc

Don't get me wrong..I love my 95 series 1..but from what I've been reading here us series 1 owners are kinda the red-headed stepchild when it comes useful mods to gain HP as compared to the later series motors..
My question is how much realistic gain can I acquire on the engine platform?
Is it worth the trouble and cost or should I go find a nice series 111 sc vehicle and take the 260bhp and be happy and save money in the long run...Maybe a Pontiac GTP or a later GT.
Only problem is they aren't a Rivey.?

Imo the series 1 have alot more power down low, there's plenty of members on here that have done extensive mods to series 1 m62 with great results, hopefully someone will chime in. I'd do anything to keep interest in your riv, they are so unique are hard to come by nowadays. Gtp, regal gs, monte ss are all dime a dozen