I've tested a lot of guns with full length tubes ....and I just didn't like them because of the difference in weight issue. The ones I considered the most - were a Citori XS Skeet 20ga ( with 28ga and .410 tubes ) ....and a Citori XS Skeet 12ga with 20ga, 28ga and .410 tubes ....both guns were 30" barrels.
In the 12ga Citori XS Skeet with 30" barrels and adj comb - the gun weighs about 8.5 lbs ...but when you put the full length tubes in it ...it added about 10 - 12 oz ...so it went up to between 9.25 and 9.5 lbs ...making it a little clumsy ( as a skeet gun, sporting clays guns ).
In the 20ga Citori XS Skeet with 30" barrels and adj comb - the gun weighs about 7.5 lbs ...so again adding the 10-12 oz for tubes ...it goes up to about 8.25 lbs .../ so as a stand alone 20ga ...its way lighter than the same model 12ga ( 8.5 lbs ) ...but with the tubes in it for 28ga and .410 it felt pretty good.
In the 20ga ...when you go to a 28ga tube set ----they're really thin / same on a 12ga when you go to a 20ga tube set ( they're thin ) ...and occasionally there will be cracking issues around the extractors / ejectors on the thinner tubes...
Bottom line ...unless I was going to spend the money for a carrier barrel and do it right ...I decided tubes were not my best option. So I ended up buying a stand alone XS Skeet 20ga, and a stand alone 28ga and a stand alone .410 ... This was a few yrs back / and I guess in all 4 guns (actually I have 5 - because I have a backup gun in 12ga as well / all in the Citori XS Skeet models, and 30" barrels ---- the 20ga, 28ga and .410 are all built on the 20ga receiver )....but I've got about $ 15,000 in replacement cost today on all 5 guns - or call it $12,000 for 4 guns. So you have to weigh the $ 12,000 for 4 guns ...against the cost of a carrier barrel and subgague tubes and chokes ...etc ..( and I'd say with a carrier barrel and everything its about $ 20,000 ) ....so its a little cheaper with stand alone guns ....but its an inferior system ...even though I've tried to weight all 4 guns so they are identical ....they're still just a hair different...and the triggers in all 4 guns are pretty good ...but not identical...
So its kind of an apples to oranges thing ....both work / or all 3 work ....the single stand alone with tubes is not the best ( too much weight difference), stand alone guns means you have to pack up and carry 4 guns around ..and they're close but not perfect ....and the carrier barrel option - which is pretty close to perfect but a little more money.
http://thefiringline.com/forums/attachment.php?attachmentid=62169&d=1281543688
So here are my primary guns --- all Citori XS Skeet models, 30" barrels top one is the 12ga, then 20ga, the 28ga and the .410 ....and since my semi-serious days of competition are over ...frankly, I like having 4 stand alone guns ...not having to fuss with tube sets...etc. But in your case - if you really want to get into this in a big way / the carrier barrel is really the way to do / and its an investment - that I think you will get your money out of long term as well - if you take care of the gun and the tubes, etc.
Now - I do like a heavier gun for Trap ...where I go to an XT ( Citori XT with 32" barrels at around 10lbs ...and I have one that is a stock gun with adj comb and one with a GraCoil and a fancy upgraded stock that I bought used ...) and I like them both ...and I can shoot them in skeet and sporting ...but they are really clumsy ( in my buddies words / they're like trying to swing a big ole sewer pipe ) when I was just fooling around and shooting skeet with the one with the GraCoil one day ...just for laughs.
http://thefiringline.com/forums/attachment.php?attachmentid=61928&d=1280945127
Both nice guns ...just not a good sporting or skeet gun, in my opinion.