For slayer and training, bunyip is good enough. Uni is overkill like above. The only tasks I used to Uni are skelewyvern, gorak , and wadever hard hitting mobs that I dont prot melee. Besides boss hunt fruit bat > Uni in some case :thumbsup:
It really depends on how long you play, if you piety and black mask and superset , you should get 100k xp per hour if you get good task (eg. fire giants) So you need to find 39 hours to play before 12 march.
use the combat calc http://www.tip.it/runescape/?page=combat_calc.htm Fill in your wadever stats except strength then let them calculate your level and how many more str lvl you need to get to the next combat lvl. HP in f2p pking not that important. Because when 1v1 fighting you keep your hp at like say 40? all the time (or else you r safer and opponent refuse to fight you or something). But then if your are low hp 40hp might be like 60% of your hp bar. (looks like safer) So meh find some value inbetween