My VP30 is also pretty much capping out at line3x, although, it is nice to have it handle transitions between interlaced and progressive video modes on the fly as opposed to direct feeding a capture card/device which will crap out as soon as the game switches video modes (maybe not all capture cards/devices, but it seems a very common theme that people have looked for a solution and solved with the DVDO products). Possibly others with different DVDO models can provide some more encouraging feedback.
It is fun getting to line4x and beyond, but sometimes the best solution is not 1920×1200. In fact, even different games on the same system will look better/suit your tastes better in one multiplication mode while others look better/suit your tastes better in a different multiplication mode. But even at pass-thru, the simple benefit of low-lag digitization offered by the OSSC really is a nice feature.
Just offering my humble opinion, and from my experience, finding the best all around solution for whatever you’re accomplishing with the OSSC may not be full line5x all the time, but the results will still be dazzling.
:edit: BUT the VP30 can take lower multiplication modes and scale them up to 1080p.