Best way to get SEO friendly URLSs on huge old website

[SCL-SEO]

Hi folks

Hope someone may be able to help wit this conundrum:

A client site runs on old tech (IIS6) and has circa 300,000 pages indexed in Google. Most pages are dynamic with a horrible URL structure such as

_http://www.domain.com/search/results.aspx?ida=19191&idb=56&idc=2888_

and I have been trying to implement rewrites + redirects to get clean URLs and remove some of the duplication that exists, using the IIRF Isapi filter: http://iirf.codeplex.com/

I manage to get a large sample of URLS re-writing and redirecting (on a staging version of the site), but the site then slows to  crawl. To imple,ent all URLs woudl be 10x the volume of config. I am starting to wonder if there is a better way:

1. Upgrade to Win 2008 / IIS 7 and use the better URL rewrite functionality included?
2. Rebuild the site entirely (preferably on PHP with a decent URL structure)
3. Accept that the URLS can't be made friendly on a site this size and focus on other aspects
4. Persevere with the IIRF filter config, and hope that the config loads into memory and the site runs at a reasonable speed when live

None of the options are great as they either involve lots of work/cost of they involve keeping a site which performs well but could do so much better, with poor URLs.

Any thoughts from the great minds in the SEOmoz community appreciated!

Cheers

Simon

[BenRWoodard]

I am going to be watching the responses here because determining the value of different ranking factoring aspects seem so subjective.  We all know what elements are important.  But, determining the level of priority in the whole scheme of things is a judgement call based on the bottom line, skill sets, and a company's ability to invest the time and resources.

From the sounds of it you aren't only dealing with hours of billable time but also on the possibility of losing sales because of the bloat that would take place while making the changes.  I would say a slower site would have a much more drastic effect than ugly URL's.  I would also say that pages with ugly URL's still do ok in search as long as there is good site architecture, quality, and unique content.  That is what I would concentrate on under your current system.  Then I would probably look at weighing the options of moving CMS.  That isn't easy either.  Migrations always take a hit on rankings, visitor loyalty, and page authority.  You will probably come out much stronger but it would be an investment.  (experienced first hand)

Just my 2 cents.

[SCL-SEO]

Many thanks Ben - and sorry for slow response!

I'm now planning on doing a simple hand coded re-write for some key terms, and monitoring the results/impact. Good call re: slow site is much worse than ugly URLS - totally agree on that. A migration is inevitable, its a case of 'when' not if (CMS is bespoke and ageing) and I'm hoping re-writes/re-directions on some of the higher traffic pages may help reduce the hit when the migration happens.

Cheers

Simon