Hi again Andrew , the secret is dont try to high magnifation , thats a myth , I only ever go to 200-250x on a really good night using my 127mm APO .
The secret is dont listen to magnifaction as a selling point , eg. 675x .. that sort of power is never used even by the largest scopes , as you will be magnifying the turbulence in the atmosphere 675x as well .. geeks ! . thats like viewing thru 2 metres of clear fast running water , all over the place and very blurry .
For your scope a 20-25mm plossel , at around 25x for low power deep sky ( where a 102 f/5 will be at its best ) and a 7.5-10mm giving 50-60x for higher powers on the moon and planets and if you want a 2x barlow to double these powers . Most newbies dont realise that 80-150x is higher power viewing and gives the best compromise .
Let us know what you decide.
Brian.