sholum: The time limit really is a killer. This is less Japanese speed reading specific and more general, but do you happen to subvocalize when you read? That is to say, do you vocalize words in your head what you are reading or something like that? That's how I am when I read and write (even as I'm typing this), but it tends to slow me down quite a bit. When I'm able to stop the subvocalization I'm able to read a lot faster but sometimes I'll have to go back and re-read something if it starts not making sense since I don't read often or practice speed reading techniques much. Also knowing how to selectively skip unnecessary details in a paragraph helps speed things up but that can be a little dangerous.
I think the amount of time it takes to read a page will be highly dependent on the reader and the material so that's kind of tough to say. I personally am a slow reader but if I'm reading a not too advanced novel where I understand a majority of the words then I can get through a full single page in a few minutes (< 5). You could instead try setting a self defined time limit of how much time you will spend on a single problem based on how many reading problems there are on the test (plus factoring in time needed for other areas of the exam), and study using that time as a metric. A rough count of the number of problems for each section and the time allowed for each part of the exam is available on the internet so you could come up with some kind of plan based on that.
Since you said you only finished 6 out of 10 problems: If it's a particularly difficult problem that you get stuck on then just skip it and come back later. If you lose 2 points because you ran out of time trying to solve one particularly difficult problem, then it's better to lose the 1 point from the difficult problem and get those other 2 points instead. Worse comes to worst, write down a random answer just before time runs out on any of the problems you couldn't figure out. You have a 25% chance of getting it right, so leave nothing blank.
Sorry, that's more general test taking advice instead of reading advice, but all points count!
(Edit: I decided to time myself reading since I was curious. It took me 1 minute 41 seconds to read an entire single page from the novel I've been reading lately, 宇宙の声.)
As for me, I received 新完全マスター聴解 N2 about 2 weeks ago and finished it earlier this week. It's a short book but overall it was a very useful book for me. If anyone needs to practice listening skills
(the majority of the book is based on building skills for the problems on the exam instead of throwing a bunch of problems at you that are similar to the exam) then I would recommend it. I struggled with it at first but it gets better.
After I finished that, I wanted to gauge how my studying has been going over the past 2 months so I redid all of the problems in 合格できる日本語能力試験N2. I had all of my old scores saved in an Excel file so it was easy to do some calculations and comparisons. My grades went way up in some areas (聴解 即時応答, 聴解 統合理解, 文法 文の組み立て, 語彙 言い換え類義, and some others). I bombed the 理解 内容理解（１） (200 word) reading questions since I was tired, but I did well in the harder reading questions after I took a nap and rested so I'm not stressing it. Bad days happens.
Overall, my lowest grade this time around was 66/100 on the 文法 文法形式の判断 set of problems. I only managed to improve by 2 points compared to my old score, but it's now the only set of problems that I scored below 70 points on. I'm going to work on learning and practicing new grammar as well as work on reading more. I need to work on vocab some more as well. If I can get my speed and confidence up then I feel like I can take on N2 with no problem.
Edited: 2015-06-25, 3:07 pm