I'm on the "There's no such thing as too much light" side. I used to run 384w of PC on my 20" deep 38gallon. It wasn't sufficient for SPS. They survived, and even grew, but never had anywhere near the color they have now, under 2x150w MH.
Were it my choice (and I recognize I have expensive tastes, but that's what this hobby is all about), I'd be going with 2x150w MH, and use the PCs for Actinic supplementation. You could also go with just a single 250w MH, but I don't think you'd see full light coverage at the edges. You're talking another $400, if you put a retro kit in your hood/canopy, but, to me, that's what it's going to take. Your T8s won't do anything for you at all, so I wouldn't bother chasing that path.
As far as cost: You could throw a couple hundred dollars at T5, with the intention to upgrade later, sure. I've always thought that intermediate steps are only a waste of money. That's a couple hundred dollars you could just throw at MH now, instead of "wasting" it on equipment you're not going to keep.