Mushrooms would be fine, even though they are from an anemone family they do well with all kinds of lighting. Anemone's are almost strictly photosynthetic. They take nutrition from the photosynthetic zooxanthellae within them, like many corals do.
You can't just put a higher wattage bulb in with PC or VHO, they require better ballasts to run. You might be able to add more T-5 bulbs and the ballast to run them.
Personally I would like to see you use VHO, but thats my preference. A 4 bulb 36 inch retro fit kit would fit nicely, so would a 46.5 inch 440 watt VHO retro kit, like the one I use. But then I also have 500watt MH as well for 940 watts over a 90 gallon.
I am rather T-5 illerterate so you may want to check with someone that runs them, or you can check back at your poorly advised LFS.
Only diff with T-5 vs other flouresent lighting is size really. My VHO bulbs are T-12 in size.
Thomas