The question is - which spec should I go with and which two trinkets should I use along with it. I'm currently really divided about this, since both specs seem to have their ups and down, with FFB occasionally pulling a lot more dps than arcane and vice versa even a dummy self dps test.
Right now, I'd stick with abyssal rune and Reign of the Unliving. You generally want to stick to arcane pve until you actually have a decent amount of crit (40-50% fire crit) so I would focus on generally improving your gear first. Once youre around 5.5k gs or so you can swap over. When I made my mage, I started with Charred and Flare of the Heavens, and arcane spec, and then went to fire once I got 40% crit at about 5.3. Haste isnt that important (youve got like 150 more haste than my 6k gs ffb mage that does like 15k dps) when youre FFB so swap out abyssal rune for flare once you switch to FFB.
You definitely can do FFB around 5k GS. I did it (and below). Your crit seems low for that GS (and haste high). Is that not counting Molten Armor? Are you glyphed? Is that using an actual FFB talent tree? Are you gemming SP + Haste for yellows? At lower GS, you just gem full crit, and as your GS gets higher, you begin replace the full crits with sp + crits. Then near the end you can start gemming pure spellpower if that strikes your fancy.
That said, your stats/gear seems ideal for Arcane spec, so, if you enjoy arcane, you should stick with it till you hit a wall. But if you want to go FFB, you can with minimal effort.