Interesting discussion. I am new to the server but have played mage extensively on a different WOTLK server about 4 years ago where we completed all content. Although I forgot a lot of things, I do remember a few things about Frostfire spec, as it was my favourite to play (I was arcane/frostfire). I always found mainstream fire spec boring and wanted something different (really enjoy the challenge of playing arcane in end-game raids). The build you linked above is slightly incorrect (1st one), and as pointed out you must have living bomb. Overall you play with same rotation as fire spec but using frostfire instead of fireball.
Frostfire is actually superior to conventional fire build at the end game (and the important bit is "end-game". The main mechanism why that is the case is the total of 150% bonus crit damage from Burnout and Ice Shards talents. However! (A BIG HOWEVER). Frostfire build is EXTREMELY gear power hungry and will not work or be better than normal fire build unless your stats are insane. Remember the main mechanism why its better (150% crit dmg). In other words, your mental philosophy when dpsing as frostfire - if your frostfire bolt doesn't crit every single time, no good - you're not utilising that talent power spike enough (and that is the ONLY reason frostfire will be better than fire).
These are the conditions under which frostfire will perform better than conventional fire build:
1. You must have a good base of basic stats: hit cap, healthy haste amount (global cooldown reduction capped and good base for your FFB not to be too slow)
2. Your total raid crit target must be: 70% or as near as possible (I raided with 68-70% raid crit). This IS NOT possible without ICC gear! And therein lies the problem! You achieve this high crit by careful selection of items (high spell dmg, crit rating + spirit items are extremely valuable, known as double crit items for mages). You also take food buffs for crit and if necessary other consumables. The strain of FFB spec on your gear is insane! It's the reason I loved it so much, as we were raiding ICC 25 HC weekly and I was in a position to decide which build uses my gear the most. The answer is: Frostfire!
3. You must have high base of spell power. This is a no brainer, but allow me to elaborate. With the intense pressure to build your crit, you must make sure your base spell dmg bonus is high too, because the 150% crit dmg bonus will only work well with a good spell dmg base. That is why frostfire is so heavily reliant on gear. Your gemming will be different to normal fire build. I cannot remember my hero gear set now, but pretty sure I gemmed soft/mid crit (i.e. spell dmg/crit rating gems and a few pure crit gems - but I was full ilvl 277 mage, so my base spell power was very high too).
To summarise:
1. Frostfire is only superior to fire at maximum gear potential, typically seen in T10 only.
2. Frostfire can still perform decently (but unreliably) in lower content, but inferior to fire overall. Play it if you like it only, but be prepared to do less dmg.
3. Frostfire requires more crit than fire build (it is not just about procing Hot Streak, you want almost every single hit to be a crit (150% crit dmg bonus - the game crit cap I think is 75%, so you're aiming to get as close to this figure as is humanly possible, see what I wrote above)