I installed my GFS Surf 90s in my 5120 the other day. I wanted to wait until I got you play them a bit to start a thread.
First impressions, awesome! I'm really happy with the tone I'm getting out of these, it's got a lot of what the Nashvilles were missing that I was looking for. I haven't heard Dynas through an amp, but I really want to a/b these sometime to see how close they really are. I can say that they sound a little better than the DeArmond 2000s that were in my 5129 (which I did like btw). They have a little more body, and a bit more low end than the 2000s did.
The bridge pup alone can get a little harsh, but that actually works well for what I'm looking for, I think with the right amp settings or a little tone knob roll it would be great. The neck pup sounds really good on it's own, which is something I'm not really used to. My Mean 90s were the first pups I ever liked the neck alone, followed by my TV Classic (chronologically, not by preference), but the Surf 90 really has a lot of clarity and sparkle on the neck only.
Together they sound amazing (by the way, I'm really bad at describing tone), all I know is I haven't ever been this happy with this guitar's sound. I almost felt bad for my 5120 because it never got played anywhere but my living room unplugged. It's definitely moved up the ranks, replacing my SG with Mean 90s as #2 (behind the 5129 with TVs).
Other things I did with this mod... I installed a treble bleed (100k .5 resistor, .001uF cap) and I really like it. It lets a little more through than I expected, in fact it almost acts like a bass roll off, but it works really well for me. I can turn down and still have my tone. Several other guitars will be getting this very soon!
I installed my Gretsch Chet Atkins strings. WOW! Seriously great strings. I'm really impressed with how they feel and sound. Although I'm not sure I can bring myself to drop $25 on them to use them regularly, but I might spring when I'm going into the studio.
I also installed the pickup bezels I got from a GDP member. I think they really look great, and definitely look better with these pups than the stock chrome bezels did. I highly recommend these if you're looking for something a little different with HB sized pups.
Alas, eye candy for you all.
5120 with Surf 90s album
Shot with a Sony Cybershot that we won from Huggies!