dual processor, scsi hdd, ram - how much difference does it make?

I'm currently on P3 1.2GHz 1GB RAM 60GB IDE HDD. My site's really at crawling speed during peak hours with a server load of 27-60 (top readings) dual processor, scsi hdd, ram - how much difference does it make? and about 45-60% of my 1 GB RAM is used. I'm thinking of upgrading but I'm really clueless how much faster would the following options be:

1. dual P4 (or even dual xeon) vs single P4 2.4ghz
2. 1 GB RAM vs 512MB RAM
3. SCSI HDD vs IDE HDD

Of course it'll be best to go for all of the above but aint got that much $. Any advice?

 

 

 

 

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