Do you like the Stradas? The 3.5s are significantly better, small, and would likely work pretty well in that room.
The Stradas are very good speakers, their only real weakness is that they have a slightly soft top end compared to tweeter technologies, and considering that the speaker uses small woofers, is limited in terms of bass response and ultimate dynamic range.
There are a handful of great monitors that would represent an upgrade:
Usher 718 DMD
KEF R Series or Ref 201.2
The Sonus are also a little soft in the top end however they have better bass and dynamics than the Stradas.
Ariaudio: You might give Walter at Underwood HiFi a call. He might well be able to work an attractive deal for you on the 3.5s.
A monimally informative comparison. I auditioned one of the B&W floorstanders with the new diamond tweeter. I'd have no trouble choosing the 3.5. The B&W was perhaps more neutral, but the draw dropping imaging and airiness of the Gallo's drew me in a lot more. My hunch is I'd have similar thoughts with the monitors (although I think the 3.5 beets the strada through the whole range, and not just the highs).
I suspect you can do substantially better than the 3.5s MSRP new, but that might be 4k or so, not 2500. At your pricepoint, I'd take the Selah Veritas (or whatever Rick's current monitor is) over the Stradas, and possibly also the Fritz Carbon 7s. Also worth consideration are some of the Zu models; they are a great company to deal with, and often have good deals on b-stock. Amp matching might be more complex with Zu, but they are very helpful and worth a call. Ditto Selah and Fritz: good guys all.
One further thought, Ariaudio.
You don't want to make a lateral move, and you've got a budget of around 2-2.5k. But the speakers you own, the Stradas, are very good at that pricepoint, and you've got a sub to compensate for their main weakness. Give the quality of your current set up, and your target price, I think you'd have to get pretty lucky to make anything but a lateral move. You could certainly get a *different* sound that you like better, or improvent in a particular respect, but obvious, all around, improvement will be harder to come by.
I think you'd be well served by patience, and careful watching of the used market: your budget get's you into speakers with north of 5k MSRP, and that presents a wealth of options. Even this way, pretty hard to beat what you've got, but definitely more likely, and you'll have fun shopping.
3k used will by a lot of speaker, especially for a smaller room. (I used ti have a room like yours; a bit hard to know how to think of sizes in open floor plan.) You might start researching new speakers up to 7k or so, where there will be tons of choices. Are any of the shows, like RMAF, close to you?
Meanwhile, you've got nice speakers!