It also depends on what else you have to interface to. Are you going to be displaying TIS traffic from the 330 on an EFIS or an MFD like a GMX200? Do you currently have enough space in your radio stack or is there going to be a lot of metal cutting or moving other radios?
If you don't already have a GTX330 I have a nearly-new one for sale. It only has bench test time on it, still has the plastic covering the display. It's not an ES but it would be priced so you could do the ES upgrade back in the Garmin shop and still come out ahead of the game.