Quad G5s (and similar HW) are getting particularly anemic at the web, and those are by far the fastest PPC systems. I can't imagine a single 700 MHz G4 would be pleasant for browsing the web at all. I agree with the sentiment that you could appreciate the machine for what it's good at, and not trying to force it into things it can barely do. (Macs aren't the best choice for this scenario anyways - the ecosystem moves a lot quicker and it's not as flexible for these things.)
Also, upgrading /to/ a 3GS in 2016? Huh?
I don't know that I would agree with that.
I have few web browsing issues on Quads provided that I stay away from flash-heavy sites. Youtube is perfectly doable even up to 720P-my Quad can manage with no stuttering or dropped frames.
I'm not an anti-Intel zealot. My first Mac was a late 2011 13" MBP, and I've since upgrade to a mid-2012 non-retina 15"(hi-res matte screen). I have 16gb of RAM and a Samsung SSD in the 15", and while it's not as fast as a Retina with PCIe drives and other architecture improvements, it's still a pretty darn fast computer. My work computer is a Mac Pro 1,1 that I've upgrade pretty extensively, including going to dual quad core processors, 16gb of RAM, a Geforce 8800, and SSDs for storage. It is showing its age, but is still perfectly usable.
Most of my PPC computers are hobby computers. I do, however, use a Quad at work to run some software for which I can't afford(and my work can't afford) an Intel equivalent. IT has been cracking down pretty hard on SL users, so my Quad mostly stays offline. I have a dual 2.7 at home that I use a lot for scanning work, but it's also a perfectly comfortable computer for web browsing and the like.