I agree with pretty much everything said here. Bigger, longer, hotter and girthier is better.
I went with a Vastex a few years ago for my first conveyor. It's done pretty well for me and I'm amazed that such a short dryer can do so well at curing ink. This is totally unsubstantiated but I think they might put really nice IR panels in the Vastex units, it would explain how a panel smaller, with less wattage than my flash can deliver a full cure in less time than it takes to flash a T. It would also explain the crazy warranty on the panels. Our EC-I can just barely stay ahead of me printing solo and I work at anywhere from 75-150 pcs/hour typically, depending on the colors and flashes in the print. We maxed it out doing heart prints with a team of three at about 350 pcs/hour. The 30" belt is very nice but you'll always want a wider belt.
If you go short on the dryer get the digital temp control it's not really an option, it's critical in my opinion. We had the model with the 'baseboard heater' style temp 'control' and it's just way too slow to get the temp under actual control. Some people like the dry-box series from them but without the PID control I say don't bother. On short dryers your print is in there for, well, a short amount of time. If the panel temp isn't spot on during that 30 seconds or whatever it might be then your going to under or over cure significantly. Long dryers, this is less of an issue I would imagine- a slow temp control has the whole 8' or so to catch-up and stabilize the temp. Most long chamber IR dryers are closed in and insulated as well so you have ambient heat happening. The Vastex concept is more like 'zap it' than 'cook it' - I guess it's the microwave oven of print dryers.
Why is no one microwaving their shirts???
Anyways, I'm actually selling the EC-I soon, about 2 weeks if all goes well. So here's a shameless plug, you can pm or email me if interested.
Down the road I want nothing but a big 'ol natural gas dryer. The M&R Heatwave is the only one I know of that will fit in you space but it's going to cost a lot more than IR.
Don't even run the dryer until you vent it. No point in breathing all that crap. I vent our chamber with a 250cfm in-line fan ('heat-moving' fans at {insert big-box home supply store here}) and then a 250cfm vent box that I made from entirely reclaimed materials- a kitchen vent fan, some sheet metal and ducting- which works surprisingly well.