I use a 30 gramme ESSS on mine with 10ft poly leaders and find that it works just fine. I would agree that you would feel the rod load more with a higher grain weight but, like a lot of modern rods these days, It has quite a wide grain window (you adjust your cast to suit).
I use my 13ft Loop Cross for my 8/9 (34/35gramme) set up, but I've read and spoke to other people who prefer to use 37/38gramme lines on it. It really depends on your casting style in my opinion and you can also throw in the confusion of different line manufacturers interpretations on line ratings.
I also use a rio scandi short versitip in 8 weight and this works fine.
Hope this helps, but it's only my opinion and I'm by no means a casting "Guru".
If it helps any, I have the 12ft 6 ins 7 weight Hardy Zenith, as all Hardy rods, it needs a line weight up on it's recommended rating(in this case an 8 weight!)
I use a Barrio 7/8 ISS Spey line, 510 Scandi compact, 510 Rage and 8 weight Rio SSVT. If your rod is more 8/9 the 8 weight SSVT might be a touch light?- thats certainly worth the thinking about?
One thing in the SSVT, they are a 1/2 way house between a Scagit and a Scandi line, they are certainly clumpy in their std. form and very prone to skipping anchors etc as they're a short powerful line!.You will find that if you walk the SSVT path the line will perform to its best with at least a 5ft poly. of an appropriate density on the end of any of its existing 10ft sinking tips. It will perform better still with a 10ft poly. in place!
On my Zenith I prefer the Scandi 510 compact(Airflo) when I want to use a shooting head or the Barrio ISS 7/8 when I want a full line.Both go like stink and will carry/turn over any poly. and tube combo you may well wish to use(within reason!, lead core and 4" of brake piping might be a tadge too much!).
Any way, cracking rods!, Pedro.