The only time I have problems with RP swamping is if I get a lot of KMRimes in a short period of time. Although, RP swamp isn't necessarily a super bad thing, it lets us interrupt and use defensive CD's like AMS or IBF without blowing the rotation.

If it really bothers you that much, I guess you could put FS above BS in priority.

That might be your problem right there, stop using that glyph. Its not so good for this spec.

Overflowing on RP seems like an odd situation though. I mean basic math can be used on this.
Assuming you use the basic rotation:

IT>PS>OB>BS>BS
OB>OB>OB

The first 10 second you generate: 15+10+20+10+10 = 65 RP
That means you have RP for 2 frost strikes. Blood Presence has room for 6-7 GCD per 10 seconds. If you assume 6 then you take 33 RP to the next 10 seconds.

The next 10 seconds is 60 RP, with the 33 from last time thats 93 RP, which is just short of 3 FS.
The problem is mostly that people burn Rime procs without having KM up. That gives RP and loses you a GCD.
Thats probably a major reason why Rime is not used (much or at all) unless KM is also available.

Another way you can cap on RP is if you use AMS, but that's a different ballgame.

Also if you have trouble with your GCD and RP dumping, i suggest you move to a more smooth rotation.

IT>PS>OB>BS>BS
OB>OB>OB

^That is a very crude rotation actually for several reasons:
1. You have 5 "runic" GCD in the first part and 3 in the second.
2. You swap between single and double rune usage, and even though that is handled somewhat by rune cushioning it still means you sometimes have to wait a split second for a rune.
3. You have 1 obliterate in the first part and 3 in the second. Therefor your rime procs have a much higher chance to overlap in the second part. Not only that, in the first part you have a bigger chance of a KM proc without rime up, and in the second part a rime proc without KM up.
4. You have a lot of RP you have to tag along to the next 10 seconds because of limited GCD.

My suggestion is moving to the 4/4 rotation that simply goes like this:

OB>OB>BS>BS
OB>OB>IT>PS

Its very easy to start as well:

IT>PS>OB>BS>BS
OB>OB>PS>IT

Use those 2 first and then you can simply move into the 4/4 rotation. This was used back in the days as well by frost 2H builds. (before the IT spam builds became popular).

Of course the setup sequence is somewhat lower dps, so i would advice against it on bosses that are dynamic. But on tank spank fights, this should be somewhat better.

There is a little delay between the mainhand and offhand hits of abilities. Easily testable when you kill some random lvl80 mob with ~10k HP, put two diseases on the target and hit OB. Most of the time the mob will die from just the mainhand damage, the offhand damage will not appaer on screen or in your combatlog. I doubt this is latency related (I always play with 60-100ms). It's fine though on targets with more HP/raid bosses, the delay won't matter there.

I was just messing with it on a dummy, and I think this is when Rime procs off the delayed OH swing plus the normal latency I described a page or two back. Basically, it means we're losing Rime procs (because you've already obliterated again by the time the proc shows up), and wasting KM procs (by doing FS and burning KM before Rime appears). Particularly with 3/5 KM, it's very frustrating trying to execute a KM HB. I'm still curious whether the sim models ToT as both hands striking immediately, or if it accounts for the delay on the OH and the complications that brings.