If you're looking for Ku-band reception, I would dump the 6' and go with a good 1.2m offset (SatelliteAV has very a very nice unit, but shipping is costly). It's a very rare FTA prime-focus dish that can beat a 1.2m offset on Ku. A prime-focus' surface accuracy is usually not adequate and finding a LNB(F) that matches is not easy. I have looked at "prime-focus Ku LNBFs", but have reservations. They tend to be specified with a f/D of 0.5-0.7, which will horribly under-illuminate any prime-focus dish. However pictures suggest their actual f/D may be lower.
I experimented around for a couple of years with a 6' Fortec petal dish. On C-band, especially with a single orthomode feed, it was a good performer when very carefully tweaked. I could get nearly everything my larger dishes received, including DVB-S2. There were 1-2 FEC 9/10 DVB-S2 feeds that were on the edge and a small number of signals where the 6' couldn't discriminate adjacent orbital interference. However it became our workhorse C-band dish and spent most of its time on 58W where it got everything.
I had some success with the 6' on Ku, but in the end it rarely measured up to my 1.2m offsets. I tried a dual orthomode feed, both stock and with customizations for Ku, and an Invacom ADF-120 Ku-only feed with C120 flanged LNBs. The ADF-120 is truly an adjustable prime-focus feed, and it convinced me there was no future for Ku on my 6'. It didn't help that the 6' polar mount was pretty sloppy mechanically, and unable to grasp a 3" OD pole tightly enough to withstand the winds I endure.
Last week I retired the 6' because I got tired of climbing on the roof every time we had a wind storm. If it had been mounted in a better shielded location and the city ordinances allowed it, I would have continued to use it for C-band. Instead I put up a 2.6m Birdview prime-focus in a more accessible location on the roof. I have put a fair amount of time into adapting my dual ortho to work with this dish and am getting good results on both C and Ku (I have a thread about this in the C-band subforum). This is the first time I have a prime-focus dish beating my 1.2m offsets. The Birdview is alleged to have an accurate surface, however my 1.8m offset beats the 2.6m Birdview. This could be a limitation of the dual ortho feed. Someday I would like to test my ADF-120 on the Birdview and resolve this question once and for all.