I wouldn't use a 6 WF on that rod because you will have to work a lot harder to get the rod to load properly with it. It can be done, but it really takes a hard, fast stroke to do it and you are going to end up using that harder, faster stroke all day long. Talk about really wanting to wear yourself out, this is the way to do it.
If, however, you put a 6 wt salmon/steelhead taper line on the rod, it would be fine because the salmon/steelhead line has a much longer belly/back taper so it carries a lot more weight once you get out to 40' and beyond than the standard 6 WF line, which has a belly of only 30' whereas the salmon/steelhead line has a belly of about 45' give or take a few feet.
Personally, I look at buying one of the cheaper WF 7 lines line the SA Air Cell, Cortland 333, or one of other cheaper WF lines on the market.