Disclaimer: I'm also not on Beta. In the following, I'm going to assume we want to maintain 100% DoT uptime, and both DoTs have a 12s duration.
Energy bar is 100<->0<->100
On live, you can get roughly 70% of your Nukes to benefit from Eclipse, but being stunned, or having to move will really mess that up.
In Cata, that number should be around 64%, and go up slightly if you spend time on things on other than nukes
1) 11% of time spent casting SS -> Benefits from Eclipse
2) 11% of time spent using the energy that SS gave us -> Benefits from Eclipse
3) 24% of time spent not casting nukes (maintaining 2 short duration DoTs, using other cooldowns, some latency)
4) 27% of time spent casting a nuke to increase energy (no benefit from Eclipse)
5) 27% of time spent using that energy (benefits from Eclipse).
76% of the time we're casting a nuke, and 49% of the time we're casting a nuke that benefits from Eclipse. 49/76 = 64% of our nukes get Eclipse. If we get stunned or have to move, items (1) and (2) don't change very much, (3) increases, and both (4) and (5) shrink. This all assumes you manage Eclipse so that it is always up when SS comes off of CD. With an effective 17s CD on SS (2s cast + 15s cooldown) that should not be too difficult.
Full-speed, wall-to-wall Eclipse means Eclipse is up 50% of the time, so each DoT would only benefit from Eclipse 25% of the time. If you maintain each Eclipse for 40s (you can use Wrath to extend Lunar, and SF to extend Solar), total Eclipse uptime climbs to 80% (10s to proc, 40s active) and each DoT benefits from Eclipse 40% of the time. The difference in total DPS is not that large though (probably one or two%).
Note that longer Eclipse means less frequent Euphoria procs. There is a tradeoff between DPS and mana. I don't know if mana will matter.
It may be (somewhat doubtful), that they will allow you to stick to one Eclipse (exit Solar Eclipse after 45s at 85 solar energy, cast a single SF and proc Solar Eclipse again). If they allow that, one DoT and one Nuke get 100% Eclipse uptime. Last DPS numbers I saw (Hamlet's 7/31 spreadsheet) showed
IS > MF
Wr > SF
and also showed that Wrath consumes energy a bit more slowly than either SF or SS generates it. Put all that together, and you'd want to go for 100% solar uptime. Our stronger DoT would see 100% Eclipse. Nukes would see >65% Eclipse, and it would always be the stronger nukes (Wrath and SS) seeing Eclipse.
Relevart
posted: saying that tooltips indicated 37% bonus from Eclipse at starter gear levels.