The short answer is Yes. You can run GPUGRID and WCG on the same computer using a GPU and a CPU respectively.

Technically speaking however, the GPU Tasks do require some CPU usage, so it will impair the CPU tasks, but typically by about 10% or less. I find that the present GPU tasks only require about 5% CPU usage on a mid range GPU (GT 240). This only rises slightly to present top end NVidia cards (GTX260 - GTX295), but of course it requires a descent CPU. A weaker CPU would use more time, say 20% of a single 2GHz core. All that said, the GPU does more work, so it is worth sacrificing some CPU time to facilitate GPU work.
Most people that run GPU tasks orientate their work towards the use of a GPU rather than the CPU. As such I keep one corefree for overhead and GPU work. The result is that it expedites GPU work. I lose 1 core per CPU but the increase in GPU speed more than make up for it (in terms of points & Task turnover) on the GPU tasks.

My overall WCG Country rank (42) is actually better than my overall Boinc country rank (88 - edit 60) which includes some GPU tasks. Although my worldwide GPUGrid rank is actually 200 (edit 120) overall (RAC 25), that is because GPUGrid is a relatively small project with far fewer participants than WCG (perhaps only 2500 active and I would guess that more than half the results come from the top 300 RAC users).
All that said, one of my GT 240 NVidia GPU cards gets me 14K Boinc points per day and uses 60W electric in doing so. Yep, thats like leaving one extra lightbulb on. An i7 would perhaps bring home about 4K to 4500 Boinc points per day. A GTX 295 would bring home ten times that.
You are right to suggest that it is like comparing apples to pairs, because GPUGrid tends to work on macro-molecular work rather than tertiary or quaternary interactions, but both have a place in Science and complement each other by giving scope (depth).

Thanks skgiven for your explanations. I have still to think about. At the moment I have a lot of GPU power unused. GTX 285, 280, many 260. But all these boards will increase an already non negligible power consumption. I have no particular interest in global BOINC ranking as many projects do not interest me much. There are a few nevertheless but they do not use GPU like Malariacontrol. I have still not made my mind with GPUGRID. I have to study more in detail what they do and how it contributes not only to pure science but to more specifically targeted causes.

Unfortunately not.
With setting 250 names per page and some dichotomy you could have saved lots of pages. I could find your 250-name page in about 10 hits.
But I agree that showing team and country ranks clearly in our My Grid pages would certainly seem normal, same as showing the rank clearly in all those lists...

MY WCG All Time UK RANKINGS (and the numbers)
- Runtime 69th (17:318:20:45:51)
- Points 38th (16,043,938)
- Results Returned 54th (27,674)

YESTERDAYS UK RANKINGS
- Runtime 9th (0:028:12:33:48)
- Points 9th (64,361)
- Results 11th (97)

I have had no more attainable badges to chase for some time, so I eased off crunching for the WCG and I am chipping in elsewhere a bit more. I'm mainly just crunching NRW tasks here - reached 4 years now.

I did the same and found my name much quicker, but now it is in the middle of a 250-line list. Now all we need is to have the list numbered.

Cheers