Coming from a Noob
Ok guys, I can say that i'm no where near as clued up about paintball equipment as you, but i've recently started, and I decided to buy a gun, now I had opted to buy the SP ION, but the shop that I went too hadn't got it in stock, so I put my hand a little deaper into my pocket and reached out a few more notes, and said i'll have the SP ION XE instead, well all I can say is it's a cracking first gun, even though i've never had any other decent guns, I think it's good price for what it is, first time I used it I got a bit carried away!
See when i've been Paintballing before i've tried to preserve my paint, and 200paintballs last me about 2x 10min rounds, maybe 3 at a push. But within the first 5mins I wend to 200, couldn't believe it, not because it's inacurate or anything infact I think it's very accurate, it's just the fact that it was my new gun and like most people wanted to give it a proper hard go! I think if i had more money on me I could have easily shot well other 500 paintballs in the first round. As a standard gun I think it's really good, i've never used or even seen the proto gun your talking about so I can't comment on that but I thought if I told you about my experience of using the ION XE you'd get an idea from a Noob's point of view. But at the same time there are some upgrades for it like the BlackHeart Board and other barrels, grips and bodykits, i've not found any bodykits that I'd buy yet but I've seen some really cool looking ones for the Ion, so i'm sure in time that they will have released them for the XE as well, because I do think that part of owning a Paintball gun is so that you can show it off to other paintballers as well.
As for cleaning well really easy, with the bolt out back, had the gun cleaned in minutes, have to say it took alot longer to clean my hopper.
So from my little experience, i'd say for a first gun get the ION XE, but I'd also listen to what the other guys have to say, because of course they know alot more than I do.