We do have members here using both larger and longer-FL scopes successfully, so it can be done, but with this mount's hardware, technique will play a role.
I'm just switching up from a 4" refractor to a 130PDS, and I have work to do on mine as well. I do notice the change. The weight is up by only about 3 lbs with all my 'stuff' attached, but even the petite 130 is bulkier than my refractor, so moment arm/leverage/balance is much different.
I helped with the recent Beta and had some early issues, so my carefully-adjusted gears are off a bit. Time to break out the hex wrenches and do a tuneup, once I get past coma corrector spacing, tilt, and collimation issues with the new scope. In the meantime, even if I'm not entirely happy with my numbers from PHD2, my stars are still round, and that's what really what matters.
FWIW, the usual recommendation for camera and guidescope positioning is 6 o'clock and 12 o'clock, respectively. I have tried other positions, and while I don't like 6-and-12 (because reasons), that does seem to be least-worst for balance. I also ordered an accessory bar for the top, so I would have more freedom to move the guidescope fore-and-aft for balance.
Hope this helps...
Mounts: ES PMC-8 EXOS2, Serial
Scopes: SW 130P-DS, SV 102EDT, ZWO 60/280 Guide
Cameras: Nikon D5300, Altair GPCAM2 290M
Software: ASCOM 6.3, CdC, AstroTortilla, BYN Pro, Sharpcap, PHD2
Computer: Thinkpad x230, Win7Pro/64