I've killed Jad 2 times (lagged and lost my cape once), and gotten killed by him 7 times.
I'll give you some information on how I did it first, then I'll try and answer your questions.
The first time I killed him (march 10, 2006), I had 87 range, 70 prayer, 87 hitpoints, 83 att, 85 str, 83 def.
When I was done I had used 14 prayer potions (4), one range potion (4), and 4 sharks. I'm not sure how many arrows I used, I don;t have any record of that.
The 2nd time I killed him (october 24, 2006), I had 91 range, 71 prayer, 93 hitpoints, 93 attack, 90 strength, 86 defense.
When I was done, I had used 10.5 super restore (4)'s, one range potion (4), 0.25 saradomin brew (4), and 4/10th's of a crystal bow.
Sorry if you think I'm showing off, I'm just trying to give you a perspective on what I needed at my levels, to show you that you'll need more supplies at your level.
I do not think you should have to raise your magic level for doing fight caves because you shouldn't have to cast any spells, those methods cost far too much to do and take way longer. The only reason for raising your magic would be that your magic level also affects your magic defense according to the runescape knowledge db, so if you got hit by jad's magic attack you might survive instead of die... but if you are hit by jad's attacks you could be killed regardless of your magic level.
Same for defense and hitpoints as magic.... if you raise your defense a bit you might have a slightly higher chance of surviving if you are hit, but
ultimately it hardly matters what your defense or hitpoints level is, he can still kill you in one hit. I don't know what his max hit is, some people say it's 95, some say it's 99, but I can confirm that i
was hit 97 by his ranged attack and survived because I had drank a sara brew just before the hit and was at 108hp. Higher defence may help on waves where you have level 90's, 180's, and 360's though because you will be doing lots of running around while trying to kill the lvl 90 while not getting hit by the lvl 180, and then running around trying to get the 180 stuck behind the 360.
Attack and Str levels do not matter much at all as long as you have at least 70 to wield guthans (which you already have), because throughout most of the game after you get to the lvl 360's you will be ranging everything except the lvl 90's.
Your ranged and prayer levels are what matter the most, they will determine how long the game takes which also determines how many prayer potions you will need. It is possible to do it at your current levels of 70 ranged, and 54 prayer, but you'll probably need about 20 super restore pots (4) or more and 2 crystal bows, or about 4k bolt racks. And the game will probably take you about 3 hours.
The range bonus you have also matters quite a bit, even a slightly higher one will be beneficial. Although there may be no noticeable affect on your hits, over the time span of 2 hours it can actually save you a noticeable amount of time.
Before you do fight caves, I would suggest you get your planned levels of 80 range and 60 prayer, it would make it quite a bit more possible and you will have some room for emergency healing during jad.
I hope I helped.
